Film-developing rack



April 15 1924..

P. HIGGINSON FILM DEVELOPING RACK Filed Dec'. 6, 1922l [m/vrai; PE/PcyMaw/wam.

l TToF/YEYJ' Patented Apr. l5, 1924.

PERCX HIGGINSONfOF LOS ANGELES, CALIFORNIA.

FILM-DEVELOEING RACK.

Application led December 6, 1922. Serial No. 605,172.

To all whom t may concern:

Be it known that I, Pintor HIGGINsoN, a subject of the King of GreatBritain, resid ing at Los Angeles, in the county of Los Angeles andState of California, have invented a new and useful Film-DevelopingRack, of which the following is a specifica-v tion. y

This invention relates to the art of photography and relatesparticularly to the production of motion pictures.

Of the many devices employed in the development of motion picture film,the simple fihn rack is most extensively used, owing to thesimplicitythereof and the fact that with its use valuable film is morenearly under perfect control throughout the development process thanwhere complicated continuous development apparatus is employed.

A. further advantage of the use of these film racks is that the spacerequired for their manipulation is comparatively small and that they maybe immersed in narrow tanks, thus making it possible to employ a minimumquantity of developing solution. These racks consist of a rectangularframe having a pair of parallel bars placed at two opposing edges of theframe over which bars the film is disposed. The ease with which suchracks may be handled and the small space and small tanksfrequired withtheir use make them extremely valuable in film laboratory work.

There is, however, an objection to the use of these racks which filmlaboratories throughout the country have endeavored to overcome, thisobjection being the formation of rack spots which are portions of thefilm receiving a greater development than the remainder of the film andso called from the fact that they occur at the points where the filmbends over the aforementioned par allel bars of the rack. Positive filmsprinted from negatives having these rack spots consequently havecorresponding light spots which, if very pronounced, cause a flicker inthe projection of the film. This overdevelopment of the negative film atthose points at which it bends over the bars is ascribed to variouscauses, one of the large film manufacturing laboratories advancing thetheory' thatit is due to eonvectioncurrents in the developing solution.This convection explanation of the cause of rack spots is substantiallyas follows:

When an exposed film wound upon a developing rack of the characterdescribed is placed in the developing solution, a chemical reactionoccurs between the silver compound of the exposedemulsion coating of thefilm and the chemical elements of the developer with the result that thedevelopment of the image voccurs and a film of developing solution ofreduced strength is disposed over the face of the film due to the factthat a portion of the strength of the developing solution coming incontact with the exposed film surface is expended in the chemical actionbetween the developing solution andthe exposed emulsion coating. Thisfilm or layer of reduced strength developer being heavier than the fullstrength developer displaces, by gravitation, downwardly across the faceof the film. This movement, of course, is very slow owing to the veryslight difference in the densities of the full strength developer andthe reaction product. Naturally, as the reaction product movesdownwardly across the face of the film full strength developer fiowsdownwardly to take the place of the reaction product and comes incontact with the uppermost portion of the film, which is that portionbending over the top aforementioned bars. At the lower edge of the rackwhere the downwardly fiowing reaction product leaves the film aslightagitation of the developer is produced which causes full strengthsolution to be brought into contact with those portions of the filmwhich bend over the lower bar. Therefore, it is assumed that owing tothe portions of the film which bend over the bars being subjected tostronger developing solution than the remainder of the film, a moreextensive deposit `of silver will occur at these points of bending.

Another theory as to the formation of rack spots, and one which seems tobe supported by the practice and experiment, is that where a `film isbent around a small diameter, the pores of the emulsion are opened, thuspermitting greater rapidity of chemical action at those points. Theactual cause of rack spots may be a combination of the two abovementioned explanations, but from the inventors experience it has beenfound that the definition of the rack spot is very nearly proportionateto the curvature of the film which extent of curvature controls theopening of the pores. In other words, where the film is bent over a rodof half inch diameter a certain degree of over development or a certainexcess of silver deposit takes place over a given area which is,controlled by the diameter ot the rod. When a portion of the same lilmis turned over a rod oitl three inch diameter, the actua-l over-depositor silver is substantially the same as the deposit of the smaller arearesulting from the use of the half inch diameter` rod, but owing to thetact that this silver deposit is spread over a greater area of film, thespot produced thereby is not as evident as the spot produced by thesmall diameter bar.

By using a curved surface or cylinder O' live or sir; inch diameter overwhich to eX- tend the lilm, it is possible to make this rack spotentirely imperceptible to the human eye, and the actual difference inthe opacity ol the different portions of the film can only be detectedby the use ot sensitive instruments. A reason why racks having largediameter surfaces over which to place the film are not employed is thatthey are not easily handled, and require larger developing tanks andgreater' amounts of developing solution than the standard racks.

It is the principal object of my invention to provide a lilm developingrack which does not cause rack spots in a iilm developed thereupon, andby the use oi which a very even development of the iilm may beaccomplished.

The especial advantages ot my invention and further objects thereof willbe made evident hereinafter.

Referring to the drawing which is for illustrative purposes only,

Fig. 1 is an elevational view of my in vention having a length of motionpicture film wound thereupon.

Fig. 2 is a fragmentary enlarged section taken upon a plane representedby the line 2-2 of Fig. 1.

Fig. 3 is a fragmentary section taken substantially upon a planerepresented by the line 3-3 of Fig. 2.

1n the practice ol my invention l employ a frame 11y comprised ofvertical members 12, a central cross bar 111 and cross bars 15 placednear the extremities oit' the vertical members 11. Near each endvertical member 11 an inwardly faced recess 18 is formed in which isplaced a bearing block 19 which receives and rotatably supports a pin 20provided in the end of a roller 21.

rllhe pin 2O is integrally formed with a knurled thumb wheel 23, one ofwhich is placed at each of the ends of the rollers 21, as shown inFig. 1. The roller 21 is preferably formedof a wooden core 25 havingcelluloid spacing collars 26 and sleeves 27 mounted thereupon. Springmembers 30 mounted upon the cross bars 15 are employed to hold thebearing members 19 in rper roller 21 as indicated at 41.

outward positions and holes 32 and 33 are drilled through the ends ofthe members 11, as shown, through which pins may be inserted to providevariations in the limits of the outward travel of the bearing blocksunder the action of the spring 30. A film 35 is placed upon the rack inthe following manner: n

The rollers are first forced inwardly and pins placed through the holes32. A film 35 having an elastic member 37 attached to the end 38 thereofis then wound upon the rack by first hooking the free end of the elasticmember over a hook 39 on the upper cross bar 15. rhe elastic member isthen stretched to a considerable emtent and the winding ont the nlm`upon the rack accomplished by placing itlirst between the first twocollars 26 on the lower roller 21 as indicated at 110, then passing thefilm across the outside of the rack to the space between the second andthird spacing collars on the up- This winding action is continued untilthe entire strip of ilm is wound upon the rack; whereupon an elasticmember 43 is attached to the end la of the iilin strip 35, and theelastic 43 stretched and hooked over a hook i5 in the lower cross bar15. The pins are then removed frein the holes 32 and the springs 30allowed to torce the rollers outwardly, thus stretching the film tightlyover the rollers 21.

The rack upon which the is now wound is placed in the developing tank.The length of time required for developing 4 of film is controlled bymany different conditions, among those being the exposure of the filmand the activity of the develop ing solution, into which activity of thesolution temperature conditions enter. The average length of timeequired for the development of iilm may be assumed as being from live toten minutes. After the film has been in the solution for a short time,for example one minute, the roller 21 at the top of the rack is slightlyturned my manipulating one et the narrow thumb wheels 23, thus causingthe film to advance a short distance upon the rollers 21. lt the turningof the rollery 21 is in a lett hand direction, those portions 50 of thefilm upon the front of the rack would move downwardly while the portions51 upon the back of the rack would be carried upwardly, thus removingfrom the rollers those portions of the film which have previously beenbent thereover and bringing the adjacent pontions of the iilm into thisbent position. The turning of the upper roller 21 as hereinbetoredescribed is continued at regular intervals until the tilm is entirelydeveloped.

The length of the rack commonly employed for this purpose is, forconvenience lil() in handling, about four feet. It will be perceivedthat it is a very simple matter to obtain a movement of the filmthereupon through a considerable distance, owing to the attachment ofthe ends of the film by means of elastic members 37 and 43, ashereinbefore described. As hereinbefore stated, the amount of surplussilver deposit upOn film due to bending of the film over the rollers issubstantially the same whether or not the film is bent over asmall'dianieter or large diameter, it will be understood that byemploying a large diameter bend, the intensity of the silver deposit,may be made imperceptible owing to the distribution of the silverdeposit of a very large area. By moving the film upon the rollers 2l ofthe development raelr shown in the drawing, I obtain the same effect aswhere a large diameter bar is employed. With my in.- vention thisdeposit may be distributed, if desired, over an area having a length offrom two to four feet; therefore, making the presence of surplus silverdeposit upon the film entirely imperceptible. For practical purposes themovement of the film need not he more than five or six inches, andtherefore, where the diameter of the roller is substantially one andone-fourth inches one revolution thereof will acffomplish this desiredmovement. i

lifter the film has been developed, fixed,

and washed, and is ready for drying, the i rollers are forced all theway in against the action of the springs and pins placed through theholes 33 thus allowing the film 35 to rest loosely upon the rack so thatthe contraction thereof during drying will be unhampered.

I claim as my invention:

l. In a film developing rack, the combination ofi: a fiat frame; and aroller turnably mounted at each end of said frame over which a filmstrip may he wound upon said rack, each of said rollers comprising ashaft having collars held in spaced 4relationship thereupon by sleeves,and having a thumb wheel at each end thereof whereby said rollers may berotated.

2. In a film developing rack, the combination of: afi-at frame; fourbearing blocks, one mounted to slide in each corner of said frame; andtwo rollers, each being mounted to have each end turnl freely in one ofsaid bearing blocks.

3. In a film developing rack, the combination of: a flat frame; fourbearing blocks, one mounted to slide in each corner of said frame;elastic means for forcing said blocks outwardly in said frame; and tworollers, each being mounted to have each end turn freely in one of saidbearing blocks.

4. In a film rack, the combination of: a frame; two roller-s mounted inopposite ends of said frame and adapted to have a film woundtherearound; and means for securing the ends of said film so that it maybe shifted on said rollers during development.

5. In a film rack, the combination of: a frame; two rollers mounted inopposite ends of said frame and adapted to have a film woundtherearound; and means for securA ing the ends of said film so that itmay be shifted on said rollers duringdevelop ment by turning one of saidrollers.

6. In a film rack, the combination ofi a frame; two rollers mounted inopposite ends of said fra-me and adapted to have a film woundtherearound; and elastic means for securing the ends of said film sothat it may be shifted on said rollers during development.

In testimony whereof, I have hereunto set my hand at Los Angeles,California this 29th day of November 1922.

PERCY HIGGINSO'N.

